Extended indentation for a fastener within an air flow

ABSTRACT

A vane includes a surface with an aperture having an extended indentation at least partially therearound.

BACKGROUND

The present disclosure relates to a gas turbine engine, and more particularly, although not exclusively, to a fastener arrangement for a vane structure.

Gas turbine engines generally include a fan section and a core section in which the fan section defines a larger diameter than that of the core section. The fan section and the core section are disposed about a longitudinal axis and are enclosed within an engine nacelle assembly. Combustion gases are discharged from the core section through a core exhaust nozzle while an annular fan bypass flow, disposed radially outward of the primary core exhaust path, is discharged along a fan bypass flow path and through an annular fan exhaust nozzle. A majority of thrust is produced by the fan bypass flow while the remainder is provided by the combustion gases.

Guide vanes extend between a fan case of the fan section and a core case of the core section to guide the fan bypass flow. The guide vanes are attached to the fan case and the compressor case with a multiple of bolts which extend through a structurally capable vane platform to endure the pounding of the adjacent rotating fan blades as well as remain resistant to foreign object damage (FOD). As there may be upwards of fifty such vanes, the cumulative fastener arrangement effect may result in an undesirable aero disturbance.

SUMMARY

A flow path according to one disclosed non-limiting embodiment of the present disclosure includes a surface with an aperture having an extended indentation at least partially therearound.

In a further embodiment of the foregoing embodiment, the surface is an inner platform of a structural guide vane.

In a further embodiment of any of the foregoing embodiments, the surface is an outer platform of a structural guide vane.

In a further embodiment of any of the foregoing embodiments, the extended indentation is “tear-drop” shaped

In a further embodiment of any of the foregoing embodiments, the said extended indentation is parabola shaped.

In a further embodiment of any of the foregoing embodiments, the extended indentation is semi-conical.

In a further embodiment of any of the foregoing embodiments, a leading edge of the extended indentation is coplanar with an upper face of a fastener.

In a further embodiment of any of the foregoing embodiments, the aperture is a counterbore aperture. In the alternative or additionally thereto, in the foregoing embodiment the extended indentation extends aft of said counterbore aperture. In the alternative or additionally thereto, in the foregoing embodiment a leading edge of said extended indentation is coplanar with an upper face of a fastener. In the alternative or additionally thereto, in the foregoing embodiment the extended indentation defines a centerline generally parallel to an airfoil that extends from said platform. In the alternative or additionally thereto, in the foregoing embodiment the extended indentation is parabola shaped. In the alternative or additionally thereto, in the foregoing embodiment the extended indentation is parabola shaped.

A gas turbine engine according to another disclosed non-limiting embodiment of the present disclosure includes a fan case, a core case, an inner surface adjacent to said core case, an outer surface adjacent to said fan case, a first fastener which retains said inner surface to said core case, said first fastener mounted within a first counterbore in said inner surface, said first counterbore having a first extended indentation at least partially therearound and a second fastener which retains said outer surface to said fan case, said second fastener mounted within a second counterbore in said outer surface, said second counterbore having a second extended indentation at least partially therearound.

In a further embodiment of the foregoing embodiment, the inner surface and said outer surface defines a portion of an aerodynamic radial boundary of a fan bypass flow path.

In a further embodiment of the foregoing embodiment, a leading edge of said first extended indentation and said second extended indentation are matched to the curvature of a flowpath.

In a further embodiment of the foregoing embodiment, the first extended indentation and said second extended indentation define a centerline generally parallel to an airfoil which extends between said inner surface and said outer surface.

A method of assembling a flow path of a gas turbine engine, according to another disclosed non-limiting embodiment of the present disclosure includes mounting a fastener into a counterbore of a surface, the counterbore having an extended indentation at least partially therearound such that an edge of the counterbore is coplanar with an upper face of the fastener.

In a further embodiment of the foregoing embodiment, the method includes orienting the extended indentation generally aftwards in convergent section of the flow path. In the alternative or additionally thereto, the foregoing embodiment includes orienting the extended indentation generally forwards in a divergent section of the flow path.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1 is a schematic cross-section of a gas turbine engine;

FIG. 2 is an expanded view of a vane within a fan bypass flow path of the gas turbine engine;

FIG. 3 is an rear perspective view of the gas turbine engine;

FIG. 4 is an expanded perspective view of a vane platform with an attachment aperture;

FIG. 5 is a top of the vane platform and an attachment aperture;

FIG. 6 is an expanded longitudinal cross-section of the vane platform and attachment aperture;

FIG. 7 is an expanded top perspective view of the attachment aperture with a fastener installed; and

FIG. 8 is an expanded cross-sectional view of the vane platform and attachment aperture with the fastener installed; and

FIG. 9 is a schematic view of a convergent divergent flowpath and an extended indentation therefor.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section 22 drives air along a fan bypass flowpath while the compressor section 24 drives air along a core flowpath for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines such as a three-spool (plus fan) engine wherein an intermediate spool includes an intermediate pressure compressor (IPC) between the LPC and HPC and an intermediate pressure turbine (IPT) between the HPT and LPT.

The engine 20 generally includes a low spool 30 and a high spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing structures 38. The low spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a low pressure compressor 44 (“LPC”) and a low pressure turbine 46 (“LPT”). The inner shaft 40 drives the fan 42 through a geared architecture 48 to drive the fan 42 at a lower speed than the low spool 30.

The high spool 32 includes an outer shaft 50 that interconnects a high pressure compressor 52 (“HPC”) and high pressure turbine 54 (“HPT”). A combustor 56 is arranged between the high pressure compressor 52 and the high pressure turbine 54. The inner shaft 40 and the outer shaft 50 are concentric and rotate about the engine central longitudinal axis A which is collinear with their longitudinal axes.

Core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed with the fuel and burned in the combustor 56, then expanded over the high pressure turbine 54 and the low pressure turbine 46. The turbines 54, 46 rotationally drive the respective low spool 30 and high spool 32 in response to the expansion.

In one non-limiting example, the gas turbine engine 20 is a high-bypass geared architecture engine in which the bypass ratio is greater than about six (6:1). The geared architecture 48 can include an epicyclic gear train, such as a planetary gear system, star gear system or other gear system. The example epicyclic gear train has a gear reduction ratio of greater than about 2.3, and in another example is greater than about 2.5. The geared turbofan enables operation of the low spool 30 at higher speeds which can increase the operational efficiency of the low pressure compressor 44 and low pressure turbine 46 and render increased pressure in a fewer number of stages.

A pressure ratio associated with the low pressure turbine 46 is pressure measured prior to the inlet of the low pressure turbine 46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle of the gas turbine engine 20. In one non-limiting embodiment, the bypass ratio of the gas turbine engine 20 is greater than about ten (10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five (5:1). It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

In one embodiment, a significant amount of thrust is provided by the bypass flow path due to the high bypass ratio. The fan section 22 of the gas turbine engine 20 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. This flight condition, with the gas turbine engine 20 at its best fuel consumption, is also known as bucket cruise Thrust Specific Fuel Consumption (TSFC). TSFC is an industry standard parameter of fuel consumption per unit of thrust.

Fan Pressure Ratio is the pressure ratio across a blade of the fan section 22 without the use of a Fan Exit Guide Vane system. The low Fan Pressure Ratio according to one non-limiting embodiment of the example gas turbine engine 20 is less than 1.45. Low Corrected Fan Tip Speed is the actual fan tip speed divided by an industry standard temperature correction of (“T”/518.7)^(0.5). in which “T” represents the ambient temperature in degrees Rankine. The Low Corrected Fan Tip Speed according to one non-limiting embodiment of the example gas turbine engine 20 is less than about 1150 fps (351 m/s).

A plurality of guide vanes 60 extend between a fan case 62 of the fan section 22 and a core case 64 of a core section 66. The guide vanes 60 as utilized herein may be structural guide vanes which support the fan case 62 relative to the core case 64 as well as direct the fan bypass airflow, Fan Exit Guide Vanes (FEGVs) which only direct the fan bypass airflow. That is, although structural guide vanes are illustrated in the disclosed, non-limiting embodiment, it should be still further appreciated that other vane structures such as non-structural fan exit guide vanes, stators, case struts, fan blade platforms, and any component with a controlled surface around an attachment feature inclusive of non-aerospace components. It should also be understood that the fan case 62 and the core case 64 are engine static structure which may include a multiple of case sections or engine modules. It should also be understood that the fan case 62, the core case 64 and the plurality of guide vanes 60 which extend therebetween may be, for example, a complete module often referred to as an intermediate case. With reference to FIG. 2, the plurality of guide vanes 60 are circumferentially spaced and radially extend with respect to the engine axis A to guide the fan bypass flow (FIG. 3). Each of the plurality of guide vanes 60 are defined by an airfoil section 68 between a leading edge 70 and a trailing edge 72. The airfoil section 68 forms a generally concave shaped portion to form a pressure side and a generally convex shaped portion to form a suction side. It should be appreciated that subsets of the plurality of structural guide vanes 60 may define different airfoil profiles to effect downstream flow adjustment of the fan bypass flow, to for example, direct flow at least partially around an upper and lower bi-fi (not shown) or other structure in the fan bypass flow path. In one disclosed non-limiting embodiment, the airfoil section 68 is located between an outer platform 74 and an inner platform 76 which respectively attach to the fan case 62 and the core case 64 with one or more respective fasteners 78. The outer platform 74 and the inner platform 76 define a portion of an annular aerodynamic radial boundary of the fan bypass flowpath downstream of the fan 42.

With reference to FIG. 4, each of the fasteners 78 are received within a respective aperture 80 along an axis F. The aperture 80 is located in a counterbore 82 (FIG. 5) such that a head 84 of the fastener 78 is below a surface 86 of the platform 74, 76 (FIG. 6). In one disclosed non-limiting embodiment, an upper face 88 of the head 84 is flush with a leading edge 90 of an extended indentation 92 in the surface 86 and at least partially surrounds the counterbore 82 (FIG. 7). That is, the leading edge 90 of the extended indentation 92 is semi-circular and in a common plane P (FIG. 8) coplanar with the upper face 88 to form a scoop parabolic, hyperbolic, tear drop, or elliptical type shape. A spacer 94 may or may not be accommodated to define a height of the head 84.

In another disclosed non-limiting embodiment, the leading edge 90 of the extended indentation 92 may be defined to match a flowpath curvature of the fan bypass flow. In other words, the fan bypass flow is directed by the airfoil section 68 between the leading edge 70 and the trailing edge 72 and the leading edge 90 of the extended indentation is defined in accordance therewith.

The extended indentation 92 extends generally aft of the counterbore 82 along an axis D which is generally parallel to an axis V of the airfoil section 68. In one disclosed non-limiting embodiment, the axis D of the counterbore 82 may be tangent to the fillet-runout of the airfoil section 68. The extended indentation 92 may be “tear-drop” shaped and indented into the surface 86 in a semi-conical shape. The extended indentation 92 essentially eliminates any air dam otherwise formed at the aft edge of the fastener head 84 (FIG. 6, 7).

With reference to FIG. 9, the extended indentation 92 is illustrated both in a convergent section C and a divergent section D of a fan bypass flow path. The extended indentation 92 in the convergent section C is located in a surface S downstream of the fasteners 78. Conversely, the extended indentation 92 in the divergent section D are located in the surface S upstream of the fasteners 78. In other words, the extended indentation 92 in the convergent section C avoid an aero-dam while the extended indentation 92 in the divergent section D avoid an aero-fall. The otherwise undesirable aero disturbances are reduced along with material removal and the associated weight reduction. As upwards of fifty (50) guide vanes 60 may be utilized in the fan bypass flow path, the reduced aero disturbance and weight reduction provided by the extended indentation 92 is cumulatively significant. It should be appreciated that other aero-shaped devices such as caps or filler material may be located on or around the fastener head 84.

It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” “bottom”, “top”, and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.

It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.

The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content. 

What is claimed is:
 1. A flow path comprising: a surface with an aperture having an extended indentation at least partially therearound.
 2. The flow path as recited in claim 1, wherein said surface is an inner platform of a structural guide vane.
 3. The flow path as recited in claim 1, wherein said surface is an outer platform of a structural guide vane.
 4. The flow path as recited in claim 1, wherein said extended indentation is “tear-drop” shaped
 5. The flow path as recited in claim 1, wherein said extended indentation is parabola shaped.
 6. The flow path as recited in claim 1, wherein said extended indentation is semi-conical.
 7. The flow path as recited in claim 1, wherein a leading edge of said extended indentation is coplanar with an upper face of a fastener.
 8. The flow path as recited in claim 1, wherein said aperture is a counterbore aperture.
 9. The flow path as recited in claim 8, wherein said extended indentation extends aft of said counterbore aperture.
 10. The flow path as recited in claim 8, wherein a leading edge of said extended indentation is coplanar with an upper face of a fastener.
 11. The flow path as recited in claim 10, wherein said extended indentation defines a centerline generally parallel to an airfoil that extends from said platform.
 12. The flow path as recited in claim 11, wherein said extended indentation is parabola shaped.
 13. The flow path as recited in claim 10, wherein said extended indentation is parabola shaped.
 14. A gas turbine engine, comprising: a fan case; a core case; an inner surface adjacent to said core case; an outer surface adjacent to said fan case; a first fastener which retains said inner surface to said core case, said first fastener mounted within a first counterbore in said inner surface, said first counterbore having a first extended indentation at least partially therearound; and a second fastener which retains said outer surface to said fan case, said second fastener mounted within a second counterbore in said outer surface, said second counterbore having a second extended indentation at least partially therearound.
 15. The gas turbine engine as recited in claim 14, wherein said inner surface and said outer surface defines a portion of an aerodynamic radial boundary of a tan bypass flow path.
 16. The gas turbine engine as recited in claim 14, wherein a leading edge of said first extended indentation and said second extended indentation are matched to the curvature of a flowpath.
 17. The gas turbine engine as recited in claim 14, wherein said first extended indentation and said second extended indentation define a centerline generally parallel to an airfoil which extends between said inner surface and said outer surface.
 18. A method of assembling a flow path of a gas turbine engine comprising: mounting a fastener into a counterbore of a surface, the counterbore having an extended indentation at least partially therearound such that an edge of the counterbore is coplanar with an upper face of the fastener.
 19. The method as recited in claim 18, further comprising: orienting the extended indentation generally aftwards in convergent section of the flow path.
 20. The method as recited in claim 18, further comprising: orienting the extended indentation generally forwards in a divergent section of the flow path. 